All the currently available motors, power generators, and various kinds of electric engines include a rotor and a stator. When a motor is excited due to the effect of stator-rotor mutual induction, the motor works or generates power. Heat will be generated when the silicon steel sheets provided on the rotor and the winding coils wound on the silicon steel sheets are supplied with an electric current. The hysteresis loss (iron loss) and copper loss of the rotor would generate thermal power, which causes increased temperature and lowered efficiency of the motor rotor, and thereby limits the maximum power of the rotary motor.
A motor usually has an efficiency of 85%. The 15% loss of the motor would cause heat transfer among the motor windings, the motor stator and/or the motor housing. When operating under atmospheric pressure, the heat generated by the motor rotor is transferred to the motor housing mainly via convection. That is, the heat generated by the motor rotor is transferred to the motor housing with the air inside the motor as the heat transfer medium. By providing the motor rotor with radiating fins to cool the motor, the effect of heat transfer via convection can be maximized.
It is also possible to transfer part of the thermal loss power of the motor or the power generator to an external environment through heat conduction and radiation via the rotary shaft and bearings of the motor or the power generator. However, this type of heat transfer mechanism can only provide relatively small cooling effect. When a high-speed shaft and a thermal rotor operate in a high-temperature condition, the rotor must be cooled. Otherwise, the rotor rotating at high load is subject to burnout due to the thermal power generated by the hysteresis loss (iron loss) and copper loss.
The currently cooling systems available for motors and power generators are mainly designed to carry heat away from the stator. As to the rotor, it could not be effectively cooled since there has not been any effective heat dissipation means for rotor up to date.
In brief, the prior art motors or power generators have the following disadvantages: (1) the hysteresis loss and copper loss of the rotor thereof generates thermal power to result in increased rotor temperature and limited motor power; (2) heat tends to accumulate in the rotor; and (3) the rotor has low cooling performance.